Generally, matching networks include electrical components and circuitry selected and configured to match the output impedance of a power supply or generator to the input impudence of a load. Without a matching network, any difference between the output impedance and input impedance results in reflections or other disruptions in the electrical energy from the supply which can cause inefficiency in the power transfer, perturbations in the operation of the load, and if the difference is large enough, destruction of components in the system. Therefore, to maximize power transfer from a power generator to a load such as a plasma processing chamber, a matching network is typically used to prevent or at least reduce reflection of the electrical power signal due to an impedance mismatch between the generator and the load.
Referring to FIG. 1, a plasma processing system may include a high or radio frequency (hereinafter referred to as ‘RF’) matching network 100, a variable impedance load 102 (e.g. a plasma processing chamber), an RF generator 104, and an RF delivery system 106. The RF matching network 100 is disposed between and electrically coupled to the RF delivery system 106 and the variable impedance load 102. The RF delivery system 106 is electrically coupled to the RF generator 104. The RF matching network 100 may include electrical components typically with fixed impedance values (e.g., capacitors and/or inductors). The RF delivery system 106 may include items such as a high power coaxial cable assembly and connectors.
The RF generator 104 may provide RF energy to the variable impedance load 102 via the RF delivery system 106 and the RF matching network 100. The function of the RF matching network 100 may be to match the impedance of the variable impedance load 102 to the output impedance of the RF generator 104 and RF delivery system 106. By matching the impedance of the variable impedance load 102 to the output impedance of the RF generator 104 and the RF delivery system 106, the reflection of the RF energy from the variable impedance load 102 may be reduced. Reducing the reflection of RF energy may effectively increase the amount of RF energy provided to the variable impedance load 102 by the RF generator 104.
Conventional methods of RF matching include creating a matching network of lumped-elements or transmission lines, or combinations of both, depending on applied frequency and load-impedance values and/or range. In order to minimize losses in the matching network, elements with reactive impedances with low series resistance (i.e., high-Q), for example, capacitors, inductors, and/or low-loss transmission lines are typically used to match the variable impedance load to the output impedance of the RF generator. FIGS. 2A through 2D are more detailed schematic drawings depicting elements of the most common types of prior art matching networks 100A through 100D. The depictions show the arrangement of one or more tune components 108, 108-1, 108-2 and one or more load components 110, 110-1, 110-2 of four different types of network topologies of the RF matching networks 100A through 100D. More specifically, FIG. 2A depicts an L-type matching network including a tune component 108 in series with the load 102 and a load component 110 in parallel with the load 102 disposed between the generator 104 and the tune component 108. FIG. 2B depicts an inverse L-type network including a tune component 108 in series with the load 102 and a load component 110 in parallel with the load 102 disposed between the load 102 and the tune component 108. FIG. 2C depicts a Π-network including a tune component 108 in series with the load 102 and a first load component 110-1 disposed between the generator 104 and the tune component 108 and a second load component 110-2 disposed between the load 102 and the tune component 108, wherein both the first and second load components 110-1, 110-2 are in parallel with the load 102. FIG. 2D depicts a T-network that includes first and second tune components 108-1, 108-2 in series with the load 102 and a load component 110 in parallel with the load 102 and disposed between the first and second tune components 108-1, 108-2.
A second conventional method of matching the impedance of the variable impedance load 102 to the impedance of the RF generator 104 may utilize variable frequency matching. The impedance presented by the RF matching network 100 to the output of the variable RF frequency generator 104 may change with the frequency. By outputting a particular frequency from the RF generator 104, the variable impedance load 102 may match the impedance of the RF generator 104 and the RF delivery system 106. This technique may be referred to as variable frequency matching. Variable frequency matching may employ an RF matching network 100 that includes fixed value tune components 108 and load components 110 (e.g. fixed value capacitors, inductors and/or resistors). The values of the tune components 108 and load components 110 may be selected to help ensure that the impedance of the RF generator 104 will match the impedance of the variable impedance load 102.
Prior art RF matching networks may help reduce the amount of energy reflected by the variable impedance load. However, the inventors of the present invention have determined that in some circumstances, existing RF matching networks do not provide the flexibility to be easily and cost effectively reconfigured to handle matching different loads at different power levels. Thus, what are needed are improved methods and apparatus for RF matching.